Cathode construction



July 12,- 193s.

- c. STANSBURY CATHODE CONSTRUCTION Original Filed March 20, 1933Patented July 12, 1938 CATHODE CONSTRUCTION Carroll Stansbury,Wauwatosa, Wis., assignor to Cutler-Hammer, Inc., Milwaukee, Wis., acorporation of Delaware Original application March 20, 1931, Serial No.

524,047. Divided and this application April 21, 1933, Serial No. 667,180

6 Claims.

Thisinvention relates to improvements in gaseous electron dischargetubes of the grid controlled type, this application being a division ofmy copending application No. 524,047, filed March 20,

The present application involves a novel construction of.a gaseouselectron tube having an additional auxiliary electrode, which forms partof the system of the aforementioned application.

In the use of gaseous grid controlled electron discharge tubes it isoften desirable to arrange for a unidirectional current flow in the gridcircuit and when the source for supplying'the grid is alternating thisnecessitates employment of a rectifier to prevent the flow of current inthe undesired direction.

.An object of the present invention is to provide a tube having meanswhich obviate the necessity for employment of a separate rectifier.

Another object is to provide a unitary structure embodying a gridcontrolled gaseous electron discharge tube and a rectifier.

Another object is to provide such a unitary structure having a singlecathode.

Another object is to provide a combined gaseous grid controlled electrondischarge device and rectifier having a common cathode and separateanodes.

Another object is to provide a device of the aforementioned character inwhich the electron flow to one of the anodes is unaffected by variationsof the grid potential.

Another object is to provide a device of the aforementioned character inwhich the effect of the grid upon the electron flow to one anode isunaffected by the flow of electrons to the other anode.

Various other objects and advantages will hereinafter appear.

The accompanying drawing illustrates my invention as applied to a systemof control which forms the subject of my aforementioned application. Itwill be understood, however, that the invention is capable of variousmodifications, and that its use is not limited to the systemillustrated.

Referring to the drawing, I is an electron tube which is preferablyfilled with a gas or vapor at low pressure. Enclosed in the tube is afilamentary cathode 2, which may be of a conventional type. The cathodeis arranged with terminals by which it can be connected toa suitablesource of electrical energy (not shown) for heating it to thedesiredtemperature. A conventional anode 3 is mounted concentric withand at one end of the longitudinal axis of the cathode. The

cathode is surrounded by a preferably concentric cylindrical grid 4.This grid may be in the shape of a solid sheet completely enclosing thecathode except for an area at its upper end adjacent to the anode, ofsufiicient extent to permit an unobstructed flow of the electron stream.Mounted in the space between the grid and the cathode is an auxiliarysmall anode 5.

It will be obvious that while the discharge between the cathode and themain anode 3 is subject to control by the grid no such control isexerted by the grid upon the discharge to the anode 5.,

Furthermore the discharge to the anode can have no appreciable effectupon the control efficiency of the grid relative to the main dischargeor any appreciable effect upon the main discharge directly as long asthe cathode is capable of supplying all of the electrons which arerequired by the two discharge currents and provided that the circuits ofthe two anodes outside of the tube do not affect each others impedance.

Due to the proximity of the cathode 2 to the auxiliary anode 5 thelatter tends to heat up when the tube is in operation, such tendencybeing increased through shielding of the cathode 2 by the grid 4, whichlatter largely prevents heat radiation from the cathode. As a result,the space inside of the grid is heated to a relatively high temperatureat which the anode 5 may tend to conduct current in the undesireddirection. To prevent this, the anode 5 is preferably made of tantalumor a tantalum alloy whose surface is oxidized, as it has been found thatsuch oxidized tantalum surfaces effectively prevent electron emissionfrom a hot body and thus prevent the reversal of current in the circuitof the auxiliary anode 5.

Supply lines L and L impress alternating voltage upon the system.Cathode 2 is directly connected to line L while anode 3 is connected toline L in series with a translating device 6, the current of which is tobe regulated. An adjustable condenser having plates of opposite polarity8 and 9 is connected between the grid 4 and line L and is paralleled byan adjustable impedance II] which is preferably non-inductive. Atransformer H has an adjustable primary winding [2 which is connectedbetween the lines L and L and a secondary winding l3 which is connectedbetween the grid 4 and the auxiliary anode 5.

The apparatus functions as follows:

When an alternating voltage is impressed upon the lines L L the cathode2 becomes alternately negative and positive with respect to the anode 3,and if the grid has no voltage impressed upon it, current flows throughthe tube and the translating device 6 during the alternate half cycleswhen the cathode is negative. These alternate half cycles shall bedesignated as the working half cycles and the other half cycles thenegative half cycles. An alternating 'voltage is also impressed upon theprimary winding I2 of the transformer II, and the resultant current insaid winding induces a corresponding voltage in the secondary windingl3. This secondary winding is so connected that its terminal which isconnected to grid 4 is negative with respect to the auxiliary anode 5during the negative half cycles of the main voltage, and thus a negativecharge is accumulated on the plate 9 of the condenser during these halfcycles, the charging current flowing from plate 9 through winding l3 toanode 5, cathode 2 and over line L to plate 8.

During the succeeding working half cycle, the polarity of the cathodeand of the transformer winding reverses and the tube conducts currentbetween the cathode 2 and the anode 3 if it is not prevented from sodoing by a negative potential on the grid 4. However, since theimpedance of the circuit of winding I3 is asymmetrical due to theunidirectional conduction between the cathode 2 and auxiliary anode 5,the negative charge on the condenser plate 9 cannot flow off through theanode 5, but only through the impedance I0 back to plate 8. Byadjustment of this impedance it is possible to adjust the time which isnecessary for the negative potential on plate 9 and grid 4 to reach asufficiently low value to permit current flow between the cathode 2 andthe anode 3, and it is thus also possible to adjust the moment duringthe working half cycle when the tube begins to supply current to thetranslating device 6. By varying this moment the effective currentsupplied to the translating device may thus be varied.

It will thus be seen that the auxiliary anode 5 in combination with thecathode 2 serves as a rectifier for the grid charging circuit, while atthe same time the current which flows through this auxiliary circuitduring the half cycles when no current flows between the cathode 2 andthe anode 3, does not directly affect the current flowing between themain electrodes during the working half cycle.

It is obvious that the current supplied through the auxiliary anode maybe used in various other ways besides the use shown herein, Where it isemployed to charge a condenser, which in turn controls the gridpotential.

What I claim as new and desire to secure by Letters Patent is:

1. A gaseous electron discharge tube having a cathode, an anode, a grid,these elements constituting a main rectifier and an auxiliary anode ofan area which is negligible relative to the area of the grid and locatedin the space between said cathode and grid, said cathode and saidauxiliary anode constituting an auxiliary rectifier to functionindependently of said grid.

"2. A gaseous electron discharge tube having a cathode, an anode, a gridsurrounding said cathode, these elements constituting a main rectifierand an auxiliary anode of an area which is negligible relative to thearea of the grid and located outside of the influence of said grid inthe space between the latter and the cathode, said cathode and saidauxiliary anode constituting an auxiliary rectifier to functionindependently of said grid.

3. A gaseous electron discharge tube having a cathode, an anode, a gridsurrounding said cathode, these elements constituting a main rectifierand an auxiliary anode of an area which is negligible relative to thearea of the grid and located within said grid, at a point outside of themain discharge path, so as to be unaffected by the discharge currentbetween the cathode and anode, said cathode and said auxiliary anodeconstituting an auxiliary rectifier to function independently of saidgrid.

4. A gaseous electron discharge tube having a cathode, an anode, a gridin the form of a solid sheet enclosing said cathode, except for adischarge area adjacent to the anode, and an auxiliary anode locatedadjacent to said cathode and within said grid.

5. A gaseous electron discharge tube having a cathode, an anode, a gridfor controlling the current flow between said cathode and anode, theseelements constituting a main rectifier and an auxiliary anode having anoxidized tantalum surface, said cathode and said auxiliary anodeconstituting an auxiliary rectifier to function independently of saidgrid.

6. A gaseous electron discharge tube having a cathode, an anode and agrid surrounding said cathode, these elements constituing a mainrectifier and an auxiliary anode located in the space between saidcathode and grid, said cathode and said auxiliary anodev constituting anauxiliary rectifier to function independently of said grid.

CARROLL STANSBURY.

